C++ Variables and Datatypes

In this tutorial we will understand the concept of C++ Variables and Datatypes.

Variables

• A variable provides us with a named storage that our programs can manipulate.
• Each variable in C++ has a specific type, which determines the size and layout of the variables memory; the range of values that can be stored within that memory and the set of operations that can be applied on that variable.
• Each variable needs an identifier(name of the variable that we assign) that distinguishes itself from others.
• The name of a variable can be composed of letter, digits, and underscore(_) characters. It must begin with either a word or underscore character.
• Upper and lower case letters are distinct because C++ is case sensitive.
• E.g. int x = 5; char letter = ‘a’;

Identifiers (name that we assign to a variable or any entity in general)

• A valid identifier, is a sequence of one or more letters, digits or underscore(_) characters. Neither spaces nor puncutation marks or symbols can be a part of identifiers.
• Only letters, digits and underscores are allowed.
• Another rule is that while creating these identifiers, use of C++ inbuilt keywords is not allowed. Some keywords (for e.g. for, while, int) are reserved keywords which cannot be used as identifiers.
• The standard reserved keywords are as follows –
  • and, double, not_eq, throw, and_eq, dynamic_cast, operator, true, asm, else, or, try, auto, enum, or_eq, typedef, bitand, explicit, private, typeid, bitor, extern, protected, typename, bool, false, public, union, break, oat, register, unsigned, case, fro, reinterpret-cast, using, catch, friend, return, virtual, char, goto, short, void, class, if, signed, volatile, compl, inline, sizeof, wchar_t, const, int, static, while, const-cast, long, static_cast, xor, continue, mutable, struct, xor_eq, default, namespace, switch, delete, new, template, do, not, this

Data Types in C++

• All variables use data-type during declaration to restrict the type of data to be stored.
• Therefore, we can say that data types are used to tell the variables the type of data it can store.
• Whenever a variable is defined in C++, the compiler allocates some memory for that variable based on the data-type with which it is declared.
• Every data type requires different amount of memory.

In C++ Programming Data types can be categorized broadly in 3 types –

1. Primitive/Buit-in Data Types.
2. Derived Datatypes.
3. User-Defined Data types.

1. Primitive / Built-in Data Types

These contain the basic inbuilt data types provided by C++ itself and are futher classified as follows-

1. integral type
   • int
   • char
2. floating type
   • float
   • double
3. void

2. Derived Data Types

These contain datatypes which are built using the basic/primitive datatypes and are provided by C++ itself however they are not considered as the basic types. For example –

1. Arrays
2. Pointers
3. References etc

3. User – Defined Data Types

These datatypes are custom datatypes that we create according to our requirements. Custom datatypes can be combinations of multiple basic datatypes. For example –

1. Structures
2. Unions
3. Classes
4. Enumerations etc

C++ Data Types Diagram

Data Type, Size and Range of Primitive Datatypes –

*the value of size and range depends on the system the program is compiled on(they depend on system architecture)

Run Online

// C++ program to sizes of data types
#include<iostream>
using namespace std;
 
int main()
{
    cout << "Size of char : " << sizeof(char) << " byte" << endl;
    cout << "Size of int : " << sizeof(int) << " bytes" << endl;
    cout << "Size of short int : " << sizeof(short int) << " bytes" << endl;
    cout << "Size of long int : " << sizeof(long int) << " bytes" << endl;
    cout << "Size of signed long int : " << sizeof(signed long int) << " bytes" << endl;
    cout << "Size of unsigned long int : " << sizeof(unsigned int) << " bytes" << endl;
    cout << "Size of float : " << sizeof(float) << " bytes" <<endl;
    cout << "Size of double : " << sizeof(double) << " bytes" << endl;
    cout << "Size of wchar_t : " << sizeof(wchar_t) << " bytes" <<endl;
    
    return 0;
}

YouTube Video Tutorial Link on Variables & Data Types in C++